Due to problems such as considerable friction in the engine when not completely warmed up, warming up of the engine must be quickly completed. The early completion of warming up is especially desirable in order to achieve efficient operation by structural components with sliding parts, including the cylinder bore, piston, and crankshaft. Normally in an engine, once in-cylinder explosion has begun, engine structural components including the cylinder block and cylinder heads, as well as engine oil circulating in oil passages that are formed in these engine structural components become heated as warming up gradually progresses. To complete early warming up of such an engine in the past, an engine rapid warming up device has been proposed in which a heat storage medium is stored in a heat storage material storage chamber that is formed so as to surround the cylinder, and the heat storage medium cooled excessively starts a change of phase and heats up (Patent Document 1). The heat storage medium has characteristics such as the following. First, the heat storage medium is heated by the engine during operation and stores heat. At this time, the heat storage medium is a liquid if the temperature of the heat storage medium corresponds to the melting point thereof or higher. Thereafter, once the engine is stopped and the engine temperature decreases, the temperature of the heat storage medium also decreases. In such case, the heat storage medium does not experience a change of phase and maintains its liquid state despite the temperature falling below the melting point, and the accumulated heat is thus preserved as latent heat. In other words, the heat storage medium is excessively cooled. Then when a change of phase is triggered in the excessively cooled heat storage medium, the accumulated heat is released while a change of phase occurs from a liquid to a solid. The released heat is used to warm up the engine. The heat storage medium, which has completed a change of phase from a liquid to a solid, is heated up by the engine during operation and absorbs combustion heat and the like from the engine so as to accumulate heat again. In the engine rapid warming up device according to Patent Document 1, such a heat storage medium is accommodated in the heat storage material storage chamber provided around the cylinder in order to warm up the engine.
Meanwhile, an engine is normally mounted with a cooling mechanism such as a water jacket that circulates coolant. Regarding this point the description of the engine rapid warming up device according to Patent Document 1 notes that the heat storage material storage chamber is formed around the cylinder of the cylinder block, and the heat absorption effect of the heat storage medium accommodated in the heat storage material storage chamber cools the cylinder block side. Patent Document 1 further notes that the cylinder head side is cooled by the forced circulation of coolant flowing through the water jacket. It should also be noted that an embodiment is disclosed in Patent Document 1 wherein the water jacket is provided on the upper side of the heat storage material storage chamber.
Patent Document 1: Japanese Patent Application Publication No. JP-A-H11-182393